QGIS applications (QGIS Desktop, QGIS Browser and QGIS Server) issues
are available in Redmine.
In order to submit or comment a report, you need an OSGeo account and login.
To get started, first Create an OSGeo account.
It may require some time to have your account approved.

Before filing an issue, review the currently open issues to make sure that
you aren’t creating a duplicate. If you have additional information on an issue,
you can add it to the existing ticket. Third party plugins might also cause problems.
If you have installed any, you should also verify that the problem is
still reproducible without them.
Please don’t report multiple unrelated bugs in a single bug report.

Description - Provide a full description of the problem including steps
to repeat it; if you think the bug could be related to a certain platform
version or dependencies package version (GDAL, OGR, GEOS etc) include that
as well. If your QGIS crashes it might be useful to include a backtrace
(see below). A very important thing when reporting a bug is to boil down
a minimum example that is needed to reproduce the bug.
The chances of a bug being addressed in a timely manner is directly related
to the speed with which the developer can reproduce the bug. If you make
that hard for the developer, chances are the bug will be given up on
or ignored for quite a while.

High: a bug which has a major effect on the usability of a package or
a bug that makes QGIS totally unusable. In the form you will find also
yes/no fields to allow you detail of the issue is causing a crash or data corruption
or if it is a regression (a regression is an issue about a functionality that
used to work as expected and then stopped to work in more recent QGIS release)

Category - Choose the aspect of the application that is most closely
associated with the problem

Affected QGIS Version - Version of QGIS this issue affects

Operating System - The Operating System(s) you are using (and also their version),
i.e: Windows 7, macOS 10.12.4, Ubuntu 16.04

On Linux QGIS automatically tries to use gdb to connect to the crashing
process to produce a backtrace. But some distributions disable the possiblity
to connect debuggers to a running processes. In that case gdb only
produces a rather useless message like:

In that case you should reenable that option by setting
kernel.yama.ptrace_scope to 0 in /etc/sysctl.d/10-ptrace.conf (or
/etc/sysctl.conf or some other file in /etc/sysctl.d/) and
run sysctl-p as root. When you reproduce the crash after that,
a backtrace will be printed instead.

If you cannot reproduce the crash, there should still be a core dump in the
current directory, that can be analysed after the process has already
terminated. It’s called core (on some systems a dot and the process id is
append to the filename).

On some distributions the creation of core dumps is also disabled. In the
event that you just get Aborted instead of Aborted(coredumped) when the
crash occurs. Then you need to run ulimit-cunlimited before starting QGIS.
You can also include that in your .profile, so that it’s always enabled when
you login.

To produce a backtrace from the core file, start gdb/path/to/the/qgis/binarycore. The binary is usually /usr/bin/qgis or
/usr/bin/qgis.bin on Debian with the GRASS plugin installed. In gdb
you run bt which will produce the backtrace.

The nightly build in OSGeo4W (package qgis-dev) is built with debugging
output, that you can view with DebugView. If the problem is not easy to
reproduce the output might shed some light about where QGIS crashes.

Most of the plugins in QGIS are published in the official QGIS Plugins repository. Bugs or feature requests relative to them
must be opened in their respective bug tracking system.
For any plugin available in QGIS repository, you’ll find in its metadata a
link to its bug tracker. Otherwise, consult the plugin documentation to find
the address of the relevant bug tracking system or a developer to contact.

QGIS project provides an active web site and a rich
documentation. Despite our efforts,
if you find an out of date information, a wrong or unclear statement
or miss a valuable information, please feel free to report it.

The main sources of these documents are hosted and managed in GitHub repositories
so in order to report bugs or submit patches, you need a GitHub account and login.